This invention relates to machines for the application of electrical insulation tape to conductors and particularly to providing a high quality of taped conductors and avoiding tape breakage by maintaining uniform tension on the tape.
Electrical machines such as large motors and generators are often provided with coil conductors having an insulation on them in the form of a tape. For example, conductor strands having their individual insulation coating may be stacked together and taped, in one or more layers of insulation, forming an insulated coil turn. A representative insulating tape may be one that consists of two layers of different materials adhesively bound together, for example respectively of mica paper and a glass fiber material, which after complete wrapping is then assembled with other so wrapped conductors and subsequently applied with an exterior ground wall insulation after which the insulation is completed by a vacuum pressure impregnation of resinous insulation material. The present invention relates generally to machines and methods for the application of a tape to one or more electrical conductors.
Taping machines have been available for some time that offer a higher speed capability than can be achieved by manual taping. Such a machine is generally characterized by having a pair of heads extending around an axial location at which the conductors are passed. The heads are rotated and each has a mounting plate with a roll of tape on it. The roll of tape is pressed against the mounting plate by a spring loaded cover plate. Varying the pressure on the cover plate varies the friction and thus the tension required to cause the roll to turn. However, as winding proceeds the diameter of the roll of tape decreases with the result that the tension on the tape will vary and result in poor quality taped conductors. Unless the force is applied by the cover plate is adjusted, the tension automatically increases on the tape and it is likely to break. To avoid excessive tension variations, it has been necessary for the operator to stop the machine and readjust the tension on the cover plate over the tape roll frequently throughout operation. To be safe, these adjustments have to be made fairly frequently but the operator must judge carefully when to make adjustments and how much of an adjustment to make. It was found necessary in the use of an 8-inch roll of tape of the type described above with a mica paper layer and a glass fiber layer, the 8-inch roll having a total length of about 800 ft., that it was necessary to perform three or four cover plate adjustments during the course of running out the 8-inch roll in order to insure sufficiently uniform tape tension. These stoppages for adjustments of tension, or stoppages for breakage, result in a serious loss in productivity.
The present invention solves these problems by modifying existing machine as it is commercially available (No. 1010 Turn Taping Machine-CNC, Lexington Sales & Engineering Co., Inc., Louisville, KY.) in order to make the tensioning of the tape independent of the quantity of tape on the roll. The modification is such that the tape roll is allowed to run free, that is, if the previously used mounting plate spring loaded cover plate is present at all it is deliberately made quite loose so it is not applying any pressure of significance against the roll. The modification of the machine from that formerly used principally consists of the provision of a tape tensioning device that is also on the head or mounting plate but which is separate from the tape roll. This tape tensioning device may, quite easily and simply, be a wheel over which the tape passes en route to the conductors. The tensioning wheel is spring loaded against a friction clutch that acts as a brake on the tape, thus creating tension on the tape as it is wrapped around the coil wires. The tape tension is controlled by adjusting the spring pressure, such as by an adjusting nut. The tensioning wheel is supported on a bearing on a shaft that may be threaded into the mounting plate. The exterior surface of the wheel may be a material such as neoprene rubber that provides adequate friction for rotation with the tape as the tape is pulled due to the rotation of the head around the conductors. The tensioning wheel has a fixed diameter and runs at a constant speed in relation to the speed of rotation of the head. Thus the tape tension remains constant regardless of the tape roll diameter.
In addition, the invention includes the provision on the mounting plate at a location independent of the tape roll and the tensioning wheel of a free wheel or idler which serves to determine and fix the location of the tape path prior to its reception at the tensioning wheel. The free wheel makes sure this tape path is constant so that there remains throughout operation a substantial portion of the tensioning wheel in contact with the tape, such as to an extent of at least about 90.degree. of the tension wheel's diameter or circumference. This means there is always a sufficient portion of the tape in frictional relation with the tensioning wheel to control the tension and that this portion is not changed as the tape roll diameter decreases.
It has been found that through the use of the present invention taping may proceed without interruption through the entire roll of tape having an original diameter of about 8 inches. Each time a roll is changed or a new roll is applied to the machine there is no disturbance of the setting of the tensioning device. It is simply necessary to remove the core of the old roll and thread the new tape through the tape path that includes going around the free wheel and around the tensioning wheel before being received at the conductors.
As the invention came about as a result of a clear need to improve the performance of the existing equipment it is apparent that it is readily retrofittable into such existing equipment as well as to such taping machines of new manufacture.